The Sun is getting back into the swing of things: a big active region on its limb erupted yesterday (October 10), sending out a small storm of subatomic particles into space. We weren’t in the line of fire, but over the next few days the rotation of the Sun will bring Active Region 11112 closer to the center of the Sun’s disk, and if that region erupts it may send a storm our way.

This shows the Sun in ultraviolet (where activity can manifest itself) from around 23:00 UT (19:00 Eastern US time) on October 11. The active region is pretty obvious there to the lower left.

A magnetogram, which shows magnetic activity, makes the region obvious as well. A recent one (shown here on the left) from around the same time as the image above again shows the active region has a lot of magnetic activity going on.

The Sun’s magnetic field lines can contain a huge amount of energy. As the gas in the Sun roils and swirls, the field lines get tangled together. If they connect, bang! They can explode, sending that energy out into space. The blast of particles can carry a magnetic field with it; if that connects to the Earth’s magnetic field, it can dump some of that energy onto the Earth. We’re safe here on the Earth’s surface, but really violent solar eruptions can damage satellites and potentially cause harm to astronauts on the space station (who have to take refuge in a better protected part of the station until the storm ends, usually in a few hours).

What’s funny is in visible light, not much can be seen from this region! Here’s the Sun taken using a filter that only lets through blue-green light:

You can see the sunspot there in the lower left, but it sure looks innocent, doesn’t it? Hmmm.

Now, to be clear: I don’t think we have much to worry about here. If that sunspot decides to throw a hissy fit, it’ll probably only create a pretty light show in the north latitudes; an aurora borealis. But as we saw in previous solar cycles, the Sun can be nasty sometimes. Hopefully we won’t be seeing any of that! But we’re on our way to the maximum of the solar cycle, sometime in 2013 or 2014. We’ll see what happens then.

Not every day, but some days yes. Green is an important color, after all. It has the narrowest frequency range and the one that our eyes are most sensitive to gradations of. (Roughly speaking, of course — all of this is somewhat subjective.) Presumably it’s no coincidence that it’s also a local maximum of the sun’s average output and the color of many nutritious-yet-immobile life forms.

… our eyes have evolved to combine light from the whole spectrum and make it look white.

Yes, assuming that “the whole spectrum” actually means the whole visible spectrum. Myself, I often wish the visible range was more than just a tiny little snippet of the whole spectrum (that just happens to coincide with the range in which both water and our atmosphere are transparent).

For me personally, Zubeneschmali does sometimes appear green although at other times appearing white – not sure whether imagination and or atmospheric affects are in play here too!

Incidentally, located about 2 degrees from Zubeneschmali is Gliese 581 (aka Gl 581 or GJ 581) a nearby (20 ly) red dwarf star with a fascinating planetary system of six worlds which includes three planets hailed as possible abodes for life – Gl 581 c, d, and most recently g. C is probably too hot and more a gas dwarf than a rocky earth-like world. d too is too massive and might be too cold but g is three to four earth masses and in the habitable zone where water can be liquid so is the most earth-like world found yet. It’s still a very different planet from ours though with many uncertainties yet to be resolved.

Antares B is another example of a green star although many think that’s just due tocontrast with the red supergiant primary star. Interestingly enough both Zubeneschamali and Antares B have the same spectral class of B8 V.

I’ll just add that our own Sun does sometimes appear green – albeit just for a fraction of a second or so during the Green Flash phenomena occassionally seen at sunsets & sunrises!

Mind you, that’s not all our Sun but only a corner of it and very temporary instant .. & I don’t think you can quite turn the world upside down to escape the “Davy Jones Locker” dimension during that like one of the ‘Pirates of the Caribbean’ movies suggested, alas.

Messier Tidy Upper: a fair point, I would say. Close to the equinoxes the aurorae should be good in both hemispheres. Further from the equinoxes you have to go to whichever hemisphere is having winter as it’s hard to see aurorae in daytime

However the number of people who’ve ever seen the aurora australis must be much smaller than those who’ve seen the aurora borealis as there just isn’t much land/population in the high southern latitudes.

Mind you, the aurora generally only appears in those locations as a suffuse pinkish and sometimes greenish glow, but I have personally witnessed a ‘pink glow’ aurora in Melbourne that was bright enough to have a few thousand people calling in to report a large ‘fire’.

Presumably it’s no coincidence that it’s also a local maximum of the sun’s average output and the color of many nutritious-yet-immobile life forms.

Sorry, but if I understand you correctly, you are wrong.
Plants are green because they do NOT use the green part of the spectrum. They absorb and consume all the other light-forms and reflect the green part, hence they look green.

OK, maybe it is really just me, but while the term “sub-atomic particles” may be technically correct, I would still call them atomic particles. Not atoms, obviously, because atoms consist of atomic particles like electrons, neutrons, protons and so forth. So, if the sun emits protons, for example, it emits atomic particles. Why the need to add “sub”? Is this a result of decades of Star Trek techno-babble…? I might be wrong, so let me know.

@#9. Messier Tidy Upper: Or anyone else with that knowledge, for that matter:
How would one pronounce ‘Gliese 581′, ‘properly’? ‘Gliese Five Eight One’, ‘Gliese Five-Eightyone’ or something else I can’t come up with?

Sorry for the rather random off topic question, but that kinda bugged me for a while now

@Messier & csrster:
csrster, you’re correct that it’s easier to see the aurora at night, and there’s certainly more of that during winter than summer; however, the reason for that is the axial tilt of the planet. During each hemisphere’s summer, that hemisphere’s pole points more closely at the sun (obviously not directly at it, but 23 degrees is nothing to laugh at). The result is that the aururae are more intense in the summer than the winter.

I would love to see Aurora. But living around 34N makes it difficult… even more so than Shoeshine boy. Add in the Terrible light pollution around here and it makes it a fairly unlikely proposition around here.

The sun must be in it 11 year cycle where there are a lot of sunspots. By the way Phil , you did’nt mention it in your Bad Astronomy book , there are some who say that massive sunspot activty caused droughts and extrem wheather on Earth now there is no conclusive evedice of this there have been studys in this . We know that sun spot activy causes raido wave disruption and incressed Aurora activey but so far there is no proof that sunspots efect the weather .

This article is disguising the very real threat posed by CMEs (Coronal Mass Ejections) … as happened in 1856 and again in the 1920s, what limited power lines there were burned, including telegraph cables, and early DC as well as AC transformers.

Now imagine all of your power going off for days, weeks, months….. years? You get the picture.

DrFlimmer, Brian and you are both half right. The sun’s max output is in green and plants reflect that color, making them appear green. There’s reason behind why they reject that color, though. Green light is too powerful and it would burn the leaves of plants if they were to absorb it. That’s why things like black roses don’t exist (or are super rare), they burn themselves to death.

@#9. Messier Tidy Upper: Or anyone else with that knowledge, for that matter: How would one pronounce ‘Gliese 581′, ‘properly’? ‘Gliese Five Eight One’, ‘Gliese Five-Eightyone’ or something else I can’t come up with? Sorry for the rather random off topic question, but that kinda bugged me for a while now.

No worries – good question.

Honestly, I’m not sure myself & wish I could answer it better for you.

The name comes from it being (I think) the five hundred and eighty-first star in the catalogue of nearby stars produced by Wilhelm Gliese back in 1957 and additional volume in 1969. (source : wikipedia links appearing soon – hopefully.) That would suggest five hundred and eighty one is correct.

That noted, there’s also the precedent set in Star Trek with Wolf 359 that also seems to be commonly heard with spelling out the numerals individual thus three-five-nine / five-eight-one.

I’m really not sure. As long as folks understand which star we’re talking about it probably doesn’t matter overly but the use of numbers in place of proper star names is a pet gripe of mine. At least its only a managable three numbers not a whole string of them like in many other cases.

Interestingly, the fact that seems that Gliese 581 is often shortened to GJ 581 would indicate it was from the second later volume of Gliese’s listing co-written by Richard van der Riet Woolley and associates or later still Hartmut Jahreiss.

Is it a good or bad thing that “Star Trek” is cited as a valid precident for Astronomical Nomenclature?

Not sure of that exactly either!

I’m being practical there in how its likely to be conventionally pronounced by others rather than meaning to imply any approval or disapproval of the sources validity.

As I noted before, I’d say (hah!) the main thing is that people understand which star it is we’re talking about. I’ve discussed this before in past threads mainly on what to call significant exoplanets and I think the catalogue names do impede communication with the public and would be better replaced with real names – not numerical codes.

I’d find that discussion for y’all now but for the fact that I need to get some sleep soon. After 2.30 am in my timezone now.

As the gas in the Sun roils and swirls, the field lines get tangled together. If they connect, bang!

makes it sound the “Ghostbuster crossing their streams”, but what needs to happen is that two sets of field lines with an angle of more than 90° between them (0° would be aligned the same way, 180° is aligned in opposite directions, e.g., one going East and one going West). Such field lines repel each other, so it takes some squeezing for this to happen. And that is where the violent convection in the surface layers (“the gas in the Sun roils and swirls”) comes into play: Every now and then convection will bring field lines so close together that the very small resistance of the plasma will make a kind of “short-circuit” and perform a X-type reconnection. Think of the field lines being parallel at first: || and then being forced together in the middle )(, into an X, reconnect into an upper and a lower part (turn the sequence X )( || onto its side) rushing away from the reconnection point due to magnetic tension. The plasma will largely follow the magnetic field, which means the reconnection event can be a rather efficient plasma slingshot.
Cheers, Regner

You are, of course, correct, but I thought that went without saying…so I didn’t say it. If we couldn’t see it, it wouldn’t be part of the visible spectrum. (I’m really tempted to put a “duh!” here, but I don’t want to be insulting…)

“Myself, I often wish the visible range was more than just a tiny little snippet of the whole spectrum (that just happens to coincide with the range in which both water and our atmosphere are transparent).”

If air and water weren’t transparent at these wavelengths, then I doubt that we would have evolved to see them.

On predicting on whether a given solar event will produce aurorae visible at a given location, the magnetic latitude of the location is a better predictor than the geographic latitude of the location.
See for example http://www.swpc.noaa.gov/Aurora/